Image sensors and methods of manufacturing the same

ABSTRACT

Image sensors and methods of manufacturing an image sensor are disclosed. A disclosed photo diode may receive short wavelength light in its depletion region without exhibiting defective phenomenon such as noise and dark current. In the illustrated example, this performance is achieved by forming a trench type light-transmission layer to occupy a major surface of the photo diode so as to reduce the area available for defects on the surface of the semiconductor substrate. As a result of this reduction, the depletion region formed upon the operation of the sensor may extend toward the surface of the semiconductor substrate without concern for defects. The image sensor may be manufactured without forming a blocking layer in connection with a silicide layer.

CROSS-REFERENCE TO RELATED APPLICATION

The entire disclosure of Korean Patent Application No. 10-2002-0087900filed on Dec. 31, 2002 is incorporated herein by reference in itsentirety.

FIELD OF THE DISCLOSURE

The present invention relates to a method of manufacturing an imagesensor, and more particularly to a method of manufacturing an imagesensor in which a trench type light-transmission layer occupying a majorsurface of a photo diode is formed on an active region of asemiconductor substrate and a lightly doped impurity layer is spreadunder the semiconductor substrate around the trench typelight-transmission layer so as to improve the quality of the finishedimage sensor through an interworking operation therebetween. Also, thepresent invention relates to an image sensor manufactured by the methodof manufacturing the image sensor.

BACKGROUND

Recently, with the rapid development of the electric/electronictechnologies, various electronic devices (e.g., video cameras, digitalstill cameras, minicams adapted to personal computers (PC), minicamsadapted to mobile phones, etc.), employing image sensor technologieshave been widely developed and used.

In the conventional devices as described above, a charge coupled device(CCD) has generally been used as the image sensor. However, the CCD hasdrawbacks. For example, the CCD requires high driving voltage, andseparate additional support circuitry. Further, the CCD has highper-unit prices. As a result of these drawbacks, usage of CCDs has beenon the decline recently.

Recently, Complementary Metal Oxide Semiconductor (CMOS) image sensorshave attracted attention as an image sensor which overcomes thedisadvantages of the CCD. Since the CMOS image sensor is manufacturedbased on a series of CMOS circuit technologies, contrary to the existingCCD, The CMOS image sensor is advantageous in that it can be driven withlow voltage, it does not require additional support circuitry, it has alow per-unit price and so on.

For example, prior art CMOS image sensors are described in U.S. Pat. No.6,583,484 entitled “Method of manufacturing photo diode CMOS imagesensor”, U.S. Pat. No. 6,507,059 entitled “Structure of a CMOS imagesensor”, U.S. Pat. No. 6,495,391 entitled “Invention for reducing darkcurrent of CMOS image sensor with new structure”, U.S. Pat. No.6,372,603 entitled “Photo diode with tightly-controlled junction profilefor CMOS image sensor with STI process”, U.S. Pat. No. 6,350,127entitled “Method of manufacturing for CMOS image sensor”, and JapanesePatent No. 2000-31525 entitled “Photo diode of image sensor andmanufacturing method thereof.”

As shown in FIG. 1, a conventional image sensor, (e.g., a CMOS imagesensor), includes a photo diode 3 formed on an active region of asemiconductor substrate 1 defined by an element isolating layer 2 so asto generate and accumulate a series of photocharges through externalincident light. It also includes a signal process transistor 10 disposednear the photo diode 3 so as to carry/discharge the photochargesgenerated and accumulated by the photo diode 3 toward an imageprocessing circuit (not shown). In the illustrated example, the signalprocess transistor 10 includes, for example, a gate insulating layerpattern 11, a gate electrode pattern 12, a spacer 13 and an impuritylayer 14.

In the example shown in the drawings, N type impurities (which areindicated as N+ in the drawing) of an impurity layer 3 a for forming thephoto diode 3 are relatively heavily doped compared with a P typesemiconductor substrate 1. Thus, a depletion region (DR) formed upon theoperation of the sensor is induced to extend inside the semiconductorsubstrate 1.

The reason why the DR is induced to extend inside the substrate 1through the relatively heavy doping of the N type impurities comparedwith the P type semiconductor substrate 1 is as follows. If the N typeimpurities are relatively lightly doped compared with the P typesemiconductor substrate 1 without a separate measure so that the DRformed upon the operation of the sensor is induced to extend toward thesurface of the semiconductor substrate 1, various defects widelyexisting around a surface 1 a of the semiconductor substrate (i.e., thesurface of the photo diode) have bad effects upon the DR without aparticular limit. Therefore, a finished photo diode operating in thisfashion may exhibit various defective phenomena such as noise, darkcurrent and so on.

In contrast, if the N type impurities are relatively heavily dopedcompared with the P type semiconductor substrate to induce the DR formedupon the operation of the sensor to extend inside the semiconductorsubstrate 1 as described above, the photo diode 3 must face the problemthat light which cannot deeply penetrate the semiconductor substrate dueto its short wavelength, (e.g., blue light), cannot normally be receivedin the DR. As a result, the finished image sensor has a greatly reducedability to reproduce colors of short wavelength (e.g., blue) light.

Meanwhile, as shown in the drawing, a silicide layer 15 is additionallyformed on a part of the signal process transistor 10. For example, thesilicide layer 15 may be formed on the surfaces of the gate electrodepattern 12 and the impurity region 14 so as to improve a contact qualitythereof.

However, if separate measures are not taken, the various defects causedby the formation of the corresponding silicide layer 15 are widelygenerated on the surface la of the semiconductor substrate 1. That is,if the formation process for the silicide layer 15 is forcedly performedin the state where the surface 1 a of the semiconductor substrate 1 isexposed without any separate covering means, damage will widely occur onthe surface 1 a of the semiconductor substrate 1 by various processingshocks applied during the formation process for the silicide layer 15.

In order to resolve such problems, in the prior art as shown in thedrawing, a blocking layer 4 is previously formed on the surface 1 a ofthe semiconductor substrate 1 so as to prevent damage on the surface 1 aof the semiconductor substrate 1 caused by the formation of the silicidelayer 15 through a function of the blocking layer 4. However, whiledamage to the semiconductor substrate 1 caused by the formation of thesilicide layer 15 may be prevented in some degree by the blocking layer4, other damage caused by the formation of the blocking layer 4 willnecessarily be generated on the surface 1 a of the semiconductorsubstrate 1, which greatly degrades a characteristic of the photo diode.

Furthermore, image sensor manufacturers face not only the degradation ofthe characteristic of the photo diode 3 due to the formation of theblocking layer 4, but also the reduction in the overall processefficiency inherent in the inclusion of an additional step to form theblocking layer 4.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an end view of an example prior art image sensor.

FIG. 2 is an end view of an example image sensor constructed inaccordance with the teachings of the present disclosure.

FIGS. 3 a to 3 f illustrate an example method of manufacturing an imagesensor in accordance with the teachings of the present disclosure.

In the following description and drawings, the same reference numeralsare used to designate the same or similar components, and so repetitionof the description of the same or similar components will be omitted.

DETAILED DESCRIPTION

As shown in FIG. 2, an example image sensor includes a photo diode 23formed on an active region of a semiconductor substrate 21 defined by anelement isolating layer 22 so as to generate and accumulate a series ofphotocharges through external incident light L. The example image sensoralso includes a signal process transistor 30 disposed near the photodiode 23 so as to carry/discharge the photocharges generated andaccumulated by the photo diode 23 toward an image processing circuit(not shown). In the illustrated example, the signal process transistor30 includes, for example, a gate insulating layer pattern 31, a gateelectrode pattern 32, a spacer 33 and an impurity layer 34.

In the illustrated image sensor, a light-transmission layer 24 isembedded in the active region of the semiconductor substrate 21, (e.g.,in a formation region of the photo diode 23 of the semiconductorsubstrate 21). The light-transmission layer 24 is embedded and formedusing a trench 24 a recessed under the semiconductor substrate 21 to acertain depth as a bottom. An impurity layer 23 a, (preferably, an Ntype impurity layer), for forming the photo diode 23 is disposed underthe semiconductor substrate 21 around the light-transmission layer 24.In the illustrated example, the light-transmission oxide layer formingthe light-transmission layer 24 is selected from any one of an UndopedSilicate Glass (USG) layer, a Boron Silicate Glass (BSG) layer, aPhosphorus Silicate Glass (PSG) layer, a Boron-Phosphorus Silicate Glass(BPSG) layer, a Tetra Ethyl Ortho Silicate (TEOS) layer and a HighDensity Plasma (HDP) Oxide layer. In the illustrated example, a bufferoxide layer 24 c is additionally disposed on an etching face of thetrench 24 a so as to improve an adhesive property of thelight-transmission layer 24 to the trench 24 a.

In the illustrated example, a concentration of the impurities formingthe impurity layer 24 (e.g., N type impurities) is maintained at a levelthat is lower than that of the semiconductor substrate 21, (e.g., the Ptype semiconductor substrate (indicated as N− in the drawing)). In thiscase, a depletion region (DR) formed upon the real operation of a sensornaturally extends toward the surface of the semiconductor substrate 21.

In the prior art as described above, N type impurities for forming thephoto diode are relatively heavily doped compared with the P typesemiconductor substrate so that the depletion region (DR) formed uponthe operation of sensor is induced to extend inside the semiconductorsubstrate. This approach is followed in the prior art because, if the Ntype impurities are relatively lightly doped compared with the P typesemiconductor substrate without a separate measure so that the DR formedupon the operation of sensor is induced to extend toward the surface ofthe semiconductor substrate, various defects widely existing around thesurface of the semiconductor substrate will have bad effects upon theDR, so that a finished photo diode may exhibit various defectivephenomena such as noise, dark current and so on.

Of course, prior art photo diodes can prevent these defective phenomenon(e.g., noise, dark current and so on) to some degree, but the photodiode must face the problem that short wavelength light (e.g., bluelight) which cannot deeply penetrate the semiconductor substrate cannotbe normally received in the DR. Thus, these prior art image sensorsexhibit a greatly reduced ability to reproduce short wavelength colors.

In contrast, in the example disclosed herein, since thelight-transmission layer 24 (consisting of, for example, thelight-transmission oxide layer), is embedded and formed in the formationregion of the photo diode 23 of the semiconductor substrate 21 so that amajor surface 21 a of the semiconductor substrate 21 corresponding tothe photo diode 23 can be replaced with a surface 24 b of thelight-transmission layer 24, a defect area of the surface 21 a of thesemiconductor substrate can be naturally reduced in proportion to anoccupying area of the light-transmission layer 24. As a result, asdescribed above, even if the N type impurities are relatively lightlydoped compared with the P type semiconductor substrate 21 so that the DRformed upon the operation of the sensor extends toward the surface ofthe semiconductor substrate, various defects existing around the surface21 a of the semiconductor substrate 21 cannot have any significant badeffect upon the DR. As a result, a finished photo diode 23 may beadvantageous in that various defective phenomena such as noise, darkcurrent and so on will not be caused while the DR is extending towardthe surface of the semiconductor substrate 21.

Moreover, since the DR extends toward the surface 21 a of thesemiconductor substrate 21, the photo diode 23 can normally receive evenshort wavelength light, (e.g., blue light), which cannot deeplypenetrate the semiconductor substrate 21 in its DR. As a result, the DRmay normally generate and accumulate the photocharges. Consequently, thefinished image sensor may achieve an increased ability to reproduceshort wavelength colors such as blue light.

As shown in the drawings, in the illustrated example the N type impuritylayer 23 a forming a base of the DR surrounds the light-transmissionlayer 24 longitudinally and horizontally while maintaining itsconcentration at a lower level. As a result of this structure, when thefull-scale operation of the sensor is performed, the DR longitudinallyand horizontally surrounds the light-transmission layer 24 correspondingto the shape of the N type impurity layer 23 a and also encroaches onthe majority of the N type impurity layer 23 a as well, thereby greatlyincreasing its expansion area compared with the prior art.

As a result, the illustrated photo diode 23 is advantageous in that itcan normally receive blue light with short wavelength in its DR and itseffective area (i.e., its DR) that is reactive with light is enlarged.Moreover, a finished image sensor would have an increased ability toreproduce short wavelength colors such as blue light.

Moreover, as shown in the drawings, a silicide layer 35 is additionallyformed on a part of the signal process transistor 30, (for example, onthe surfaces of the gate electrode pattern 32 and the impurity layer34), so as to improve a contact quality thereof.

As described above, in the prior art a blocking layer 4 has been formedso as to prevent damage to the surface of the semiconductor substratecaused by the formation of the silicide layer. However, when theblocking layer 4 is formed on the surface of the semiconductorsubstrate, the manufacturers necessarily encounter the problems ofdegradation in the characteristic of the photo diode and degradation inprocess efficiency as discussed above.

In contrast, in the illustrated example, since the light-transmissionlayer 24 (consisting of, for example, the light-transmission oxidelayer), is widely embedded and formed in the formation region of thephoto diode 23 of the semiconductor substrate 21, even if the formationprocess for the silicide layer 35 is forcedly performed without forminga blocking layer on the semiconductor substrate side (i.e., the photodiode), because of the protective function of the light-transmissionlayer 24, the semiconductor substrate side will not incur any separatedamage. As a result, the manufacturers can attain the effect of normallyprotecting the semiconductor substrate (i.e., the photo diode) withoutactually forming the blocking layer. Therefore, if the additionalformation process for the blocking layer concerned with the silicidelayer is excluded from the overall process, manufacturers can avoid theproblems of degradation in the characteristic of the photo diode anddegradation in the process efficiency which would have been caused bythe formation of the blocking layer.

Hereinafter, an example method of manufacturing the image sensor asdescribed above will be explained in detail.

The example method of manufacturing the image sensor shown in FIGS. 3 ato 3 f comprises: embedding the light-transmission layer 24 in theactive region AR of the semiconductor substrate 21; ion-implantingimpurities to form the impurity layer 23 a for the photo diode 23 spreadunder the semiconductor substrate 21 while surrounding thelight-transmission layer 24; and forming the signal process transistor30 for carrying/discharging photocharges accumulated in the photo diode23.

First, as shown in FIG. 3 a, by performing a high temperature thermaloxidation process, a sacrificial oxide layer 101 (whose thickness is,for example, about 40˜150 Å) is grown on the front face of thesemiconductor substrate 21. The sacrificial oxide layer 101 serves torelieve the stress on the semiconductor substrate 21 caused by asacrificial nitride layer 102 to be formed later.

Then, by performing a low pressure chemical vapor deposition (CVD)process, the sacrificial nitride layer 102 (whose thickness is, forexample, about 600˜1500 Å) is formed on the sacrificial oxide layer 101.The sacrificial nitride layer 102 serves as a mask layer at the time ofthe formation of the trench 22 a and 24 a to be described below, and asan etch stopper layer during a chemical mechanical polishing (CMP)process.

Next, a photoresist pattern (not shown) is formed on the sacrificialnitride layer 102 so that openings of the photoresist pattern arepositioned at a part of the active region AR and at a part of aninactive region FR of the semiconductor substrate 21. The sacrificialoxide layer 101 and the sacrificial nitride layer 102 are then patternedto expose a part of the active region AR and the inactive region FR ofthe semiconductor substrate 21 by performing a dry etching process withan anisotropic feature, (e.g., a reactive ion etching (RIE) processusing the photoresist pattern as en etching mask). The photoresistpattern is then removed.

Subsequently, by performing, for example, the RIE process using theremaining sacrificial nitride layer 102 as an etching mask, a part ofthe exposed portion of the active region AR and the inactive region FRof the semiconductor substrate 21 is anisotropically etched to a certaindepth. As a result, the trenches 22 a and 24 a are formed in a part ofthe active region AR and the inactive region FR of the semiconductorsubstrate 21. The trench 22 a serves as a base of an element isolatinglayer 22 in the inactive region FR. The element isolation layer 22provides element isolation. The trench 24 a serves as a base of thelight-transmission layer 24 in the active region AR. The trench 24 aimproves the photo diode's characteristics.

Once the trenches 22 a and 24 a have been completely formed through theforegoing procedure, a thermal oxidation process is performed at, forexample, about 800˜900° C. to grow the buffer oxide layers 22 b and 24 c(having a thickness of, for example, 100˜400 Å), on the etching faces ofthe trenches 22 a and 24 a as shown in FIG. 3 a. The buffer oxide layers22 b and 24 c serve to facilitate adhesion of the light-transmissionlayer 24, (to be formed later), to the etching faces of the trenches 22a and 24 a and also serve to recover the damaged silicon latticesremaining in the etching faces of the trenches 22 a and 24 a.

Once the buffer oxide layers 22 b and 24 c have been completely grownthrough the foregoing procedure, by selectively performing, for example,a TEOS process, an APCVD process, a PECVD process or an HDP CVD process,inner portions of the trenches 22 a and 24 a are filled with a thickoxide layer S so as to cover the sacrificial nitride layer 102 as shownin FIG. 3 b. The thick oxide layer S may be, for example, a USG layer, aBSg layer, a PSg layer, a BPSg layer, a TEOS layer or an HDP oxidelayer, etc.

Then, by performing the CMP process, the oxide layer S formed on thesacrificial nitride layer 102 is planarized. The sacrificial nitridelayer 102 serves as an etch stopper layer of the oxide layer S asdescribed above.

Then, by performing the thermal process at a high temperature (forexample, about 800˜1200° C.), the oxide layer S is densified so that aninsulation characteristic of the oxide layer S is enhanced.

Subsequently, by performing a wet etching process using phosphoric acidsolution, the sacrificial nitride layer 102 is isotropically etched. Byperforming a wet etching process using HF solution, the sacrificialoxide layer 101 and the remaining oxide layer S are isotropically etchedso as to expose the surface of the semiconductor substrate 21 as shownin FIG. 3 c. At this point, the light-transmission layer 24 and theelement isolating layer 22 have been completely embedded in the trenches22 a and 24 a.

Once the light-transmission layer 24 has been completely embedded in thetrenches 22 a and 24 a through the foregoing procedure, as shown in FIG.3 d, a photoresist pattern 103 is formed on the semiconductor substrate21. An opening of the photoresist pattern is positioned at a part of theactive region AR of the semiconductor substrate 21, (for example, apredetermined portion of the photo diode 23). By performing animplantation process of impurities using the photoresist pattern 103 asa mask, the impurity layer 23 a for the photo diode 23 is formed. Theimpurity layer 23 a is spread under the semiconductor substrate 21 whilesurrounding the light-transmission layer 24. The photoresist pattern 103is then removed.

The level of concentration of the impurities, (for example, N typeimpurities), forming the impurity layer 23 a is maintained lower thanthat of the P type semiconductor substrate 21. As a result, the DRformed at the time of the operation of the sensor extends toward thesurface 21 a of the semiconductor substrate 21.

Then, by selectively performing the thermal oxidation process, lowpressure CVD process and so on, the gate insulating layer is formed onthe front face of the semiconductor substrate 21. Then by additionallyperforming the low pressure CVD process, a poly crystal silicon layer isformed on the gate insulating layer. Thereafter, by performing aphotolithography process, the gate insulating layer and the poly crystalsilicon layer are patterned together so that, as shown in FIG. 3 e, thegate insulating layer pattern 31 and the gate electrode pattern 32 areformed in the active region of the semiconductor substrate 21, (i.e.,near the photo diode 23).

Then, by performing the low pressure CVD process, an insulating layercovering the gate electrode pattern 32 is formed on the front face ofthe semiconductor substrate 21. By performing a dry etching process withan anisotropic etching feature on the insulating layer, (for example, anRIE process), a spacer 33 is formed on the sidewalls of the gateelectrode pattern 32.

Then, by performing an ion implantation with high concentration usingthe spacer 33 as a buffer mask, the impurity layer 34 is formed on theside of the gate electrode pattern 32. The formation of the impuritylayer 34 completes the formation of a finished signal process transistor30 for carrying/discharging the photocharges accumulated in the photodiode 23.

Of course, even though it is not shown in the drawings, persons ofordinary skill in the art will appreciate that the signal processtransistor 30 illustrated in the drawings can be disposed at many sitesof the semiconductor substrate 21.

By performing, for example, a sputtering process, a thin metal layer 35a, (e.g., a Ti layer), for forming a silicide layer is formed on thefront face of the semiconductor substrate 21 (including the gateelectrode pattern 32, the spacer 33, and the impurity layer 34).

Then, by performing a thermal process on the semiconductor substrate 21,the metal atoms forming the thin metal layer 35 a and the silicon atomsforming the semiconductor substrate 21 are reacted with each other. As aresult, the silicide layer 35 made of, for example, SiTi_(x), is formedon the surface of the impurity layer 34 and the gate electrode pattern32 as shown in FIG. 3 f.

In contrast to the prior art, since the light-transmission layer 24 ofthe illustrated example is widely embedded and formed in the formationregion of the photo diode 23 of the semiconductor substrate 21, even ifthe formation process for the silicide layer 35 is forcedly performedwithout forming a blocking layer on the semiconductor substrate side(i.e., the photo diode), because of the protective function of thelight-transmission layer 24, the semiconductor substrate side is notdamaged. As a result, manufacturers can attain the benefit of protectingthe semiconductor substrate (i.e., photo diode) without additionallyforming the blocking layer.

Then, by performing subsequent processes (e.g., the formation processesfor the insulating layer, the contact hole, the metallization, theinterlayer dielectric, the color pattern, the planarized layer, themicro lens array and so on), a finished image sensor is completelymanufactured.

As described above, a finished photo diode has been disclosed that mayreceive short wavelength (e.g., blue) light in its depletion regionwithout defective phenomenon such as noise, dark current and so on. Thedisclosed photo diode achieves this result by forming a trench typelight-transmission layer occupying a major surface of the photo diode onthe active region of the semiconductor substrate so as to reduce an areaavailable for defects on the surface of the semiconductor substrate sothat the depletion region formed upon the operation of the sensor mayextend toward the surface of the semiconductor substrate irrespective ofdefects.

The problems of degradation in the characteristic of the photo diode anddegradation in processing efficiency caused by an additional formationprocess for a blocking layer used in connection with the formation ofthe silicide layer are avoided by forming a trench typelight-transmission layer stably protecting the depletion region andexcluding the additional formation process for the blocking layer.

From the foregoing, persons of ordinary skill in the art will appreciatethat the above disclosed methods and apparatus provide a finished photodiode that receives short wavelength light (e.g., blue light) in itsdepletion region without defective phenomenon such as noise, darkcurrent, etc. The illustrated methods and apparatus achieve this byforming a trench type light-transmission layer occupying a major surfaceof a photo diode in an active region of a semiconductor substrate so asto reduce the area which may be occupied by defects on the surface ofthe semiconductor substrate. The depletion region formed upon theoperation of a sensor may, thus, extend toward the surface of thesemiconductor substrate without fear of defects.

The illustrated methods and apparatus also avoid degradation of acharacteristic of the photo diode and degradation in processingefficiency which are caused in the prior art by performing an additionalformation process to create a blocking layer. The illustrated methodsand apparatus achieve these advantages by forming a trench typelight-transmission layer that stably protects a depletion region formedupon the operation of the sensor on a photo diode region of asemiconductor substrate without forming a blocking layer in connectionwith the silicide layer.

A disclosed image sensor includes: a light-transmission layer embeddedand formed on an active region of a semiconductor substrate; an impuritylayer in the semiconductor substrate and surrounding thelight-transmission layer so as to form a photo diode for thegeneration/accumulation of photocharges; and signal process transistorfor carrying/discharging the photocharges accumulated in the photodiode.

Preferably, the light-transmission layer is embedded and formed in anactive region using a trench recessed under the semiconductor substrateas a bottom. Preferably, the light-transmission layer is formed of alight-transmission oxide layer including any one of an Undoped SilicateGlass (USG) layer, a Boron Silicate Glass (BSG) layer, a PhosphorusSilicate Glass (PSG) layer, a Boron-Phosphorus Silicate Glass (BPSG)layer, a Tetra Ethyl Ortho Silicate (TEOS) layer and a High DensityPlasma (HDP) Oxide layer.

In the illustrated example, the impurities forming the impurity layerare N type impurities whose concentration level is maintained lower thanthat of the semiconductor substrate.

A disclosed method of manufacturing an image sensor comprises embeddinga light-transmission layer in an active region of a semiconductorsubstrate; ion-implanting impurities to form an impurity layer for aphoto diode in the semiconductor substrate and surrounding thelight-transmission layer; and forming a signal process transistor forcarrying/discharging photocharges accumulated in the photo diode.

Preferably, embedding the light-transmission layer comprises forming asacrificial layer pattern on a part of the semiconductor substrate;etching the active region of the semiconductor substrate to a certaindepth using the sacrificial layer pattern as a mask to form a trench;forming the light-transmission layer on the semiconductor substrate tocover the sacrificial layer pattern and the trench; and selectivelyremoving the light-transmission layer using the sacrificial layerpattern as a mask to leave the light-transmission layer only in thetrench.

Although certain example methods and apparatus have been describedherein, the scope of coverage of this patent is not limited thereto. Onthe contrary, this patent covers all methods, apparatus and articles ofmanufacture fairly falling within the scope of the appended claimseither literally or under the doctrine of equivalents.

1. An image sensor comprising: a light-transmission layer embedded andformed in an active region of a semiconductor substrate, wherein atrench recessed in the semiconductor substrate is used as a bottom forthe light-transmission layer; an impurity layer in the active region ofthe semiconductor substrate and substantially surrounding thelight-transmission layer except the top surface of thelight-transmission layer to form a photo diode, wherein the photo diodehas a shape of a trench in which the light-transmission layer issituated; and a signal process transistor to carry/dischargephotocharges accumulated in the photo diode.
 2. An image sensor asdefined in claim 1, wherein the light-transmission layer is comprises alight-transmission oxide layer.
 3. The image sensor as defined in claim2, wherein the light-transmission oxide layer is any one of an UndopedSilicate Glass (USG) layer, a Boron Silicate Glass (BSG) layer, aPhosphorus Silicate Glass (PSG) layer, a Boron-Phosphorus Silicate Glass(BPSG) layer, a Tetra Ethyl Ortho Silicate (TEOS) layer and a HighDensity Plasma (HDP) Oxide layer.
 4. The image sensor as defined inclaim 1, wherein the impurity layer is formed by N type impurities. 5.An image sensor as defined in claim 1, wherein a concentration level ofimpurities forming the impurity layer is lower a concentration level ofimpurities forming the semiconductor substrate.
 6. The image sensor asdefined in claim 1, wherein the impurity layer is in contact five facesof the light-transmission layer.
 7. The image sensor as defined in claim1, further comprising a buffer oxide layer formed between thelight-transmission layer and the photo diode.